1. Field of the Invention
The present invention relates to a method and apparatus for applying composite plating (or composite coatings) such as one called NIKASIL coating, or plating, on an internal surface of a hollow member such as a cylinder of an engine.
2. Description of Related Art
A cylinder of an engine, for example, is subjected to wear, etc., on its internal side by the sliding of a piston. Therefore, it is necessary to improve the abrasion resistance or wear resistivity of the internal surface of the cylinder especially when a cylinder block is made of an aluminum alloy which easily wears. In the case where openings must be formed on an internal surface of the cylinder such as in a 2-cycle engine of a crank scavenging type, it is difficult to mount by fitting a sleeve inside the cylinder. A composite plating is sometimes applied in such a case. A known method of applying a composite plating on the internal surface of the cylinder, is the so-called NIKASIL plating in which an electrode is inserted into the cylinder with a clearance to the internal surface thereof, the clearance is filled with a composite plating liquid containing ultrafine particles of silicon carbide in a mixture with nickel sulfate, wherein the ultrafine particles of the silicon carbide are contained or enclosed in nickel.
However, in order for the ultrafine particles to be contained in a composite plating layer, the flow velocity of the composite plating liquid cannot be made very large. Therefore, the flow of the composite plating liquid in this clearance becomes a laminar flow. This will be accompanied by the following disadvantage. Namely, on an upstream side of the composite plating liquid, the ultrafine particles of silicon carbide or the like can be well contained inside the composite plating layer. However, on a downstream side, since the content of the ultrafine particles contained in the composite plating liquid close to the internal surface of the cylinder is decreased, the amount of ultrafine particles contained in the composite plating layer decreases. As a result, the composite plating layer becomes nonuniform between the upstream side and the downstream side.
As an art to solve this kind of disadvantage, there is known one by Japanese Published Unexamined Patent Application No. 93636/1977 in which the flow of the composite plating liquid is reversed at every predetermined period of time.
In the above-described art in which the flow of the composite plating liquid is reversed at every predetermined interval of time, there is a disadvantage in that the central portion is difficult of being composite-plated (or plated by the composite plating liquid), though both end portions of the cylinder may be made equal in the plating conditions. This tendency of nonuniform plating increases with the increase in the length of the cylindrical portion.